1. Field of Invention
The present invention finds principal application within the field of passive solar energy systems. More particularly, the invention relates to a sensitive check valve for use in solar panels which employ a thermosiphoning loop of liquid to convectively transfer heat.
2. Prior Art
With the dwindling supplies of fossil fuel and the accompanying increasing energy costs, extensive research efforts are being focused to harness solar radiation on a practical and economical scale. One type of device which shows promise in the field is the thermosiphon system, described in U.S. Pat. No. 4,137,964 issued to Bruce Shawn Buckley and in U.S. application Ser. No. 6,767, filed Jan. 26, 1979, by the same inventor.
As disclosed in the above references, a "thermic diode" panel is used to collect and store the sun's radiant energy. The panel typically comprises a shallow rectangular box that is effectively divided into two chambers by a slab of insulation. The chambers are filled with a liquid, such as water, and are in open communication with each other at the bottom of the panel via a passage through the insulation, and in communication at the top through flow control means, normally located outside the panel proper. A preferred flow control means discussed in the reference is an "oil valve".
Solar radiation incident on the outer panel face will heat the water in the adjacent chamber. As the water expands it passes upwardly through the oil valve and into the cooler storage chamber, setting up a thermosiphon loop. Cooler water from the storage chamber, in turn, passes through the insulation passage at the bottom of the panel to the warmer collector chamber.
If such a panel is used during the day to collect solar energy and store the heat for night time use, reverse thermosiphoning must be avoided to prevent energy loss. The oil valve achieves this objective and, in addition, increases the sensitivity of the thermosiphoning process to small temperature differences between the chambers. However, it is also desirable for the valve to permit reverse flow at high temperatures to prevent overheating and possible damage to the panel.
It is therefore an objective of the present invention to provide an inexpensive alternative to the oil valve which will function at low pressure differences, exhibit low pressure drops, prevent reverse thermosiphoning under normal conditions and permit reverse flow if high temperatures are encountered in the storage chamber.